Add base:: to string16 in extensions/.

extensions/common/error_utils.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef EXTENSIONS_COMMON_ERROR_UTILS_H_
 #define EXTENSIONS_COMMON_ERROR_UTILS_H_
 
 #include <string>
 
 #include "base/strings/string16.h"
 
 namespace extensions {
 
 class ErrorUtils {
  public:
   // Creates an error messages from a pattern.
   static std::string FormatErrorMessage(const std::string& format,
                                         const std::string& s1);
 
   static std::string FormatErrorMessage(const std::string& format,
                                         const std::string& s1,
                                         const std::string& s2);
 
   static std::string FormatErrorMessage(const std::string& format,
                                         const std::string& s1,
                                         const std::string& s2,
                                         const std::string& s3);
 
-  static string16 FormatErrorMessageUTF16(const std::string& format,
-                                          const std::string& s1);
+  static base::string16 FormatErrorMessageUTF16(const std::string& format,
+                                                const std::string& s1);
 
-  static string16 FormatErrorMessageUTF16(const std::string& format,
-                                          const std::string& s1,
-                                          const std::string& s2);
+  static base::string16 FormatErrorMessageUTF16(const std::string& format,
+                                                const std::string& s1,
+                                                const std::string& s2);
 
-  static string16 FormatErrorMessageUTF16(const std::string& format,
-                                          const std::string& s1,
-                                          const std::string& s2,
-                                          const std::string& s3);
+  static base::string16 FormatErrorMessageUTF16(const std::string& format,
+                                                const std::string& s1,
+                                                const std::string& s2,
+                                                const std::string& s3);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_ERROR_UTILS_H_